It changes fro ADSL to VDSL - and whereas there are a few modems/routers that will do both almost everyone out there is ADSL (various flavours) without VDSL capability.
Splitting the two gives BT (and others) control and access to the modem which users don't really need and BT can manage that device, whilst presenting an Ethernet connection to the user who can then choose his own router.
I have not taken a filter apart either - is it straight through on the VDSL side, or does it have a filtering capability.
M H C
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